1. field of the Invention
This invention pertains to colorable chromogenic compounds eligible for use in pressure-sensitive record material. Pressure-sensitive mark-forming record systems, single sheet and manifold, are improved by use of these compounds.
More specifically, this invention relates to chromogenic compounds having at least one benzoindolyl moiety which compounds have the form of substantially colorless or slightly colored solids, or which approach being colorless when in liquid solution; but, which may be converted to dark-colored forms upon reactive contact with acidic material. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by effecting localized reactive contact between the chromogenic material and the acidic material on or in such web or sheet, such material being brought thereto by transfer, or originally there in situ, the desired reactive contact forming dark-colored materials in the intended image-marking areas.
The chromogenic compounds of this invention have the following general formula: ##STR2## wherein A can be aminophenyl, indolyl, and benzoindolyl, substituted or not; B can be benzoindolyl, substituted or not; and E can be a broad family of aromatic and heterocyclic structures.
2. Description of the Prior Art
Several phthalide and fluoran chromogenic compounds have been disclosed. For example, U.S. Pat. Nos. 3,491,111, and 3,491,116, issued Jan. 20, 1970, disclose indole- and carbazol-substituted phthalides. U.S. Pat. No. 2,417,897, issued Mar. 25, 1947, discloses crystal violet lactone, U.S. Pat. No. 3,681,390, issued Aug. 1, 1972, discloses aryl-substituted fluorans.
U.S. Pat. No. 3,672,935, issued June 27, 1972, discloses use of colorless chromogenic compounds in pressure-sensitive record material.